The present invention relates to a spacer with a cell-formed lattice-work for retaining parallel, elongated elements such as fuel rods into a bundle in a nuclear reactor fuel assembly. In known embodiments, the spacers are normally arranged at a distance of 5-6 dm from each other along the bundle. In the arrangement referred to here, the cell-formed lattice is formed from tubular sleeves, each of which offers a passage for one of the above-mentioned elements in order to mutually fix the elements.
It is important that the spacers do not provide too high a resistance to the coolant flow which flows inside the fuel assembly along the bundle and through the spacers.
It is known to try to achieve lower spacer resistance and hence improved cooling in a boiling reactor with a fuel assembly in the form of an elongated polygonal channel in which the bundle of fuel rods is arranged. This has been done by the use of sub-spacers, each of which takes up only a part of the total cross section of the bundle and thus braces the fuel rods in this cross section only. Another known solution is to provide the bundle with spacers which alternately fix only the fuel rods positioned peripherally in the bundle (peripheral spacers), or the fuel rods located centrally inside the former fuel rods (central spacers).
The lattice-work in the above-mentioned known spacers consists of plate bands, standing on edge, which are arranged crosswise and form square cells. In certain types of reactors, this type of lattice-work provides less favourable cooling conditions than a lattice-work composed of tubular, preferably round sleeves because the sleeves can be fitted in a better way around the normally round fuel rods.